DateTime's representation in milliseconds?

Question

I have a SQL-server timestamp that I need to convert into a representation of time in milliseconds since 1970. Can I do this with plain SQL? If not, I've extracted it into a DateTime variable in C#. Is it possible to get a millisec representation of this ?

Thanks,
Teja.

Answer 1

You're probably trying to convert to a UNIX-like timestamp, which are in UTC:

yourDateTime.ToUniversalTime().Subtract(     new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)     ).TotalMilliseconds 

This also avoids summertime issues, since UTC doesn't have those.

Answer 2

In C#, you can write

(long)(date - new DateTime(1970, 1, 1)).TotalMilliseconds

Answer 3

As of .NET 4.6, you can use a DateTimeOffset object to get the unix milliseconds. It has a constructor which takes a DateTime object, so you can just pass in your object as demonstrated below.

DateTime yourDateTime;
long yourDateTimeMilliseconds = new DateTimeOffset(yourDateTime).ToUnixTimeMilliseconds();

As noted in other answers, make sure yourDateTime has the correct Kind specified, or use .ToUniversalTime() to convert it to UTC time first.

Here you can learn more about DateTimeOffset.

Answer 4

There are ToUnixTime() and ToUnixTimeMs() methods in DateTimeExtensions class

DateTime.UtcNow.ToUnixTimeMs()